Effect of cytochalasin A on actin distribution in the fission yeastSchizosaccharomyces pombe studied by fluorescent and electron microscopy

Summary Actin distribution and ultrastructure of the fission yeastSchizosaccharomyces pombe treated with cytochalasin A (CA) were investigated by fluorescence microscopy using rhodamine-conjugated phalloidin (rh-ph) and freeze substitution electron microscopy. Among the cytochalasins tested, CA was most effective and at 5 g/ ml inhibited the appearance of the actin ring at the cell equator at the stage prior to septum formation and the accumulation of actin dots at the septum-forming site both in wild-type cells and the mutantcdc 11, which is defective in septum formation at restrictive temperature. Freeze substitution electron microscopy of CA-treated cells revealed the displacement and morphological alteration of cytoplasmic vesicles and dictyosomes within 30 min and the appearance of dense bodies in the cytoplasm. A sub-population of cytoplasmic vesicles and dictyosomes were insensitive to CA and maintained their original structure. An electron less dense layer containing filamentous material was noted beneath the plasma membrane and thought to be the area of heavy actin patches stained with rh-ph at the cells ends. These results suggest that CA disrupted an actin network that normally maintains the organization of the secretory pathway involving dictyosomes and vesicles.     

Group I introns in the liverwort mitochondrial genome: the gene coding for subunit 1 of cytochrome oxidase shares five intron positions with its fungal counterparts.

The complete nucleotide sequence of the mitochondrial DNA (mtDNA) from a liverwort, Marchantia polymorpha, contains thirty-two introns. Twenty-five of these introns possess the characteristic secondary structures and consensus sequences of group II introns. The remaining seven are group I introns, six of which happen to interrupt the gene coding for subunit 1 of cytochrome oxidase (cox1). Interestingly, the insertion sites of one group II and four group I introns in the cox1 gene coincide with those of the respective fungal mitochondrial interns. Moreover, comparison of the four group I introns with their fungal counterparts shows that group I introns inserted at identical genomic sites in different organisms are indeed related to one another, in terms of the peptide sequences generated from the complete or fragmental ORFs encoded by these introns. At the same time, the liverwort introns turned out to be more divergent from their fungal cognates than the latter are from one another. We therefore conclude that vertical transmission from a common ancestor organism is the simplest explanation for the presence of cognate introns in liverwort and fungal mitochondrial genomes.     

Gene organization deduced from the complete sequence of liverwort Marchantia polymorpha mitochondrial DNA. A primitive form of plant mitochondrial genome.

Analysis of the mitochondrial DNA of a liverwort Marchantia polymorpha by electron microscopy and restriction endonuclease mapping indicated that the liverwort mitochondrial genome was a single circular molecule of about 184,400 base-pairs. We have determined the complete sequence of the liverwort mitochondrial DNA and detected 94 possible genes in the sequence of 186,608 base-pairs. These included genes for three species of ribosomal RNA, 29 genes for 27 species of transfer RNA and 30 open reading frames (ORFs) for functionally known proteins (16 ribosomal proteins, 3 subunits of H(+)-ATPase, 3 subunits of cytochrome c oxidase, apocytochrome b protein and 7 subunits of NADH ubiquinone oxidoreductase). Three ORFs showed similarity to ORFs of unknown function in the mitochondrial genomes of other organisms. Furthermore, 29 ORFs were predicted as possible genes by using the index of G + C content in first, second and third letters of codons (42.0 +/- 10.9%, 37.0 +/- 13.2% and 26.4 +/- 9.4%, respectively) obtained from the codon usages of identified liverwort genes. To date, 32 introns belonging to either group I or group II intron have been found in the coding regions of 17 genes including ribosomal RNA genes (rrn18 and rrn26), a transfer RNA gene (trnS) and a pseudogene (psi nad7). RNA editing was apparently lacking in liverwort mitochondria since the nucleotide sequences of the liverwort mitochondrial DNA were well-conserved at the DNA level.     

Pathological studies on encephalitis in mice experimentally inoculated with bovine coronavirus

One- to 21-day-old mice were examined pathologically after inoculated intracerebrally or subcutaneously with the Kakegawa strain of bovine coronavirus. In 1- to 4-day-old mice inoculated intracerebrally, the brain contained a small number of neutrophils and lymphocytes having infiltrated diffusely and perivascularly and some degenerative neurons. In mice inoculated intracerebrally at 7 to 21 days of age, severe necrosis of pyramidal cells was shown in Ammon's horn. Perivascular infiltrations of neutrophils and lymphocytes were moderate to severe. Some neurons were degenerative in the cerebral cortex, thalamus and midbrain. Degeneration of some neurons and mild infiltration of neutrophils and lymphocytes were observed in the brain of mice inoculated subcutaneously at 1 to 7 days of age. Perivascular infiltration of neutrophils and lymphocytes was prominent in the cerebral cortex of mice inoculated subcutaneously at 14 days of age. Cellular infiltration was also seen in the thalamus, Ammon's horn, midbrain, cerebellum and medulla oblongata. All the mice, except one, inoculated subcutaneously at 21 days of age were free from neural changes. Electron-microscopically, virus particles were observed in and outside of the degenerative neurons. They had a core 70 nm in diameter and an envelope with spikes.     

Seroepizootiological survey on bluetongue virus infection in cattle in Japan

Bovine sera collected in various parts of Japan were subjected to seroepizootiological tests with bluetongue virus type 1 (BTV1), type 12 (BTV12), and type 20 (BTV20). All these viruses have been widely disseminated among cattle in the southern part of Japan in 1974. Relatively high incidences of neutralizing (NT) antibody against the three viruses were shown among cattle in the Kyushu district, including Okinawa Prefecture, or the southern part of Japan, but extremely low or incidences in Hokkaido, or the northern part of Japan. The incidence of reactors was higher in old animals. Cattle in Okinawa Prefecture showed a high rate of seroconversion for all the viruses during the summer of 1979. None of the animals seroconverted, however, manifested any sign of disease. Seroepizootiological investigation made it clear that BTV1, BTV12 and BTV20 had existed in Japan and that the epizootic of bluetongue virus infection started during a period from summer through early autumn.     

Collection of rice phloem sap from stylets of homopterous insects severed by YAG laser

Pure phloem sap from rice plant was collected by a method similarto the aphid technique using leafhoppers and planthoppers instead.A Yttrium-Aluminium Garnet laser was used to sever the insectstylets. Sap exuded from the plant through the stylet for upto 3 hr at a rate of 0.2 µl/hr. Analysis of the sap forsugars revealed that the only carbohydrate present was sucrose;its content was estimated to be 17% and remained at this levelfor 3 hr. (Received April 16, 1980; )     

A contractile ring and cortical changes found in the dividing Tetrahymena pyriformis

A contractile ring consisting mainly of microfilaments was found in the fission zone of dividing Tetrahymena pyriformis. Diameters of the microfilaments were widely distributed from 2.5 to 15 nm. Ring-associated structures such as lateral stripes, linkers and beads with siender tails were recognized. Lateral stripes arranged at regular intervals of about 84 nm on some parts of microfilament bundles were found in both tangential and transverse sections, suggesting that they correspond to bands fastening the contractile ring microfilaments. Linkers that connect individual lateral stripes to the epiplasmic layer were present. Beads or beads with slender tails were found to be arranged on some microfilaments.The results of the present paper also indicate that drastic morphological changes occur in the cortex of the fission zone, especially in the epiplasmic layer, accompanying contraction of the division furrow. The epiplasmic layer which was proved to be a compact filamentous network in this study has been known to exist at the periphery of cytoplasm in immediate contact with one of the cell surface membranes, the inner alveolar membrane; however, in the fission zone of the dividing ceil, it was frequently separated from the membrane and subsided into the cytoplasm. The subsided epiplasmic layer was then loosened and dispersed. The subsidence of the epipiasmic layer appears to be caused by the force generated by the contraction of the contractile ring and transmitted with the linkers to the epiplasmic layer. The changes observed in the epiplasmic layer are presumably indispensable for the rigid cortical layer contraction involved in cytokinesis of Tetrahymena.